Abstract
Blue light (BL), absorbed by phototropin (phot), activates the plasma membrane H+-ATPase via phosphorylation of the C-terminus in guard cells, and drives stomatal opening. However, there is no biochemical evidence for early events of phot in stomatal guard cells. We isolated cDNAs encoding phot, named vfphot1 and vfphot2, from guard cells of Vicia faba. In vivo phosphorylation analysis using 32P-labeled guard-cell protoplasts revealed that vfphots were reversibly phosphorylated in response to BL, and that phosphorylation of vfphots was faster than that of the H+-ATPase. BL-induced phosphorylations of vfphots and H+-ATPase showed similar fluence dependency. Staurosporin, an inhibitor of protein kinase, and diphenyleneiodonium chloride, an inhibitor of flavoprotein, inhibited BL-induced phosphorylations of vfphot and H+-ATPase with similar concentration-dependencies. From these results, we concluded that vfphots act as BL-receptors mediating stomatal opening and that BL-induced phosphorylation of vfphots might be required for the activation of H+-ATPase.
